In assemblies of this nature it is customary to provide the constituent elements with mutually complementary male and female coupling formations referred to hereinafter as tenons and mortises. In the case of plastic elements, the tenons are molded as integral projections whereas the mortises are simply formed as undercut recesses which are laterally accessible to facilitate removal from the mold as well as insertion of a tenon from an adjoining element upon assembly.
This technique is entirely satisfactory when each structural element has its preassigned place in the completed assembly. In many instances, however, it is desirable to rearrange some of these elements or to add further components of a similar nature in order to meet different requirements, e.g. to fill up a variable area or volume. If the assembly is a mat, for example, it may have to be restructured in accordance with the ground or floor space to be covered. In such an instance, however, it may happen that two tenons or two mortises confront each other when a given component is relocated from one position to another. This makes it necessary to store a significant number of spare components to be used only for certain configurations.